1. Field of the Invention
The present invention relates to an electromagnetic actuator, such as an optical deflector, which is electromagnetically driven.
2. Description of the Related Art
For the application to drive a relatively large mirror as typified by, e.g., an optical switch in the static and analog manner, an electromagnetic drive type optical deflector is superior to a static drive type element in the drive efficiency and controllability.
U.S. Pat. No. 5,912,608 discloses an optical deflector having a gimbal structure. FIG. 30 of the present application shows a deflecting mirror element such as that used in the optical deflector of U.S. Pat. No. 5,912,608.
As shown in FIG. 30, this deflecting mirror element comprises an inner movable plate 1101, an outer movable plate 1102 arranged on the outer side of the inner movable plate 1101, a support frame 1103 arranged on the outer side of the outer movable plate 1102, hinges 1104 connecting the inner movable plate 1101 and the outer movable plate 1102, and hinges 1105 connecting the outer movable plate 1102 and the support frame 1103.
This deflecting mirror element is located in a parallel magnetic field 1108 generated by external magnets (not shown). The inner movable plate 1101 includes a coil 1106 formed on it, and the outer movable plate 1102 includes a coil 1107 formed on it. A current flowing through the coil 1106 rotates the inner movable plate 1101 about a longitudinal axis of the hinges 1104 by the interaction of the parallel magnetic field 1108. Further, a current flowing through the coil 1107 rotates the outer movable plate 1102 about the longitudinal axis of the hinges 1105 by the interaction of the parallel magnetic field 1108.
The inner movable plate 1101 has a reflecting surface 1109 formed on it. The inner movable plate 1101 can be rotated solely or together with the outer movable plate 1102 at a desired angle by controlling the current flowing through the coil 1106 and the coil 1107. That is, a direction of the reflecting surface 1109 of the inner movable plate 1101 can be controlled. As a result, a direction of a light beam reflected by the reflecting surface 1109 can be arbitrarily adjusted.
In the optical deflector having the deflecting mirror element with the gimbal structure such as shown in FIG. 30, however, it is difficult to statically and independently drive each of the inner movable plate and the outer movable plate. That is, crosstalk occurs between the rotational operations corresponding to the respective rotational axes. Description will now be given as to this difficulty, namely, generation of the crosstalk with reference to FIG. 31.
In FIG. 31, a current flowing through the coil 1106 formed on the inner movable plate 1101 can be decomposed of two components, i.e., a current component 1110 and a current component 1111. The current component 1110 generates a couple 1115 that rotate the inner movable plate 1101 about the rotational axis 1120. The current component 1111 generates a couple 1116 that rotate the outer movable plate 1102 about the rotational axis 1121 through the hinge 1104.
Accordingly, when the current is caused to flow through the coil 1106 in order to drive the inner movable plate 1101, the outer movable plate 1102 is also rotated. Therefore, it is hard to independently rotate each of the inner movable plate 1101 and the outer movable plate 1102.